The invention relates to communication of data between data processing systems in which secure data is transmitted between the systems via a secure channel. The term "secure data" means data which is confidential so that the user wishes to ensure that it has the maximum protection from unauthorised access.
It is quite commonplace for secure data such as credit card numbers to be transmitted via telephone voice channel, via fax transmissions, or using DTMF tones with a telephone. In a limited way, such communication can be quite effective. For example, there is growing use of DTMF interaction for automatic 24-hour on-line banking. This type of communication is regarded as being quite secure.
However, such communication is quite limited and cannot provide the range of services and flexibility which can be provided by systems such as PCs connected to a host system. An example is a connection to an Internet service provider.
It is also known to transmit secure data in a broadcasting system, as described in GB 2154108 (Communications Patents Limited). An arrangement is described in this specification whereby a subscriber selects a secure channel dedicated to the transmission of encrypted data and his or her terminal is temporarily connected to the secure channel. The channel is used for communication of encryption keys. The system includes a channel selector, a secure channel signal generator, and a secure channel selection detector at the head end. The user end includes a receiver, a channel selector controller, a decryptor, an algorithm store, and an encryptor. This system involves much signalling to establish communication and requires special hardware. Further, it does not appear that it would provide the necessary versatility which is required for general communication in which a large portion of the data to be communicated is not necessarily secure data.